Alternator Voltage surging

[Jerry Emert]

While on the road Thursday I noticed that the voltage gauge was surging between 12-17 volts.  Very rythmatically taking less than a second to go between 12-17.  The gauge is rock solid at 12v while the engine is off.  On start the voltage appears to be solid at 18v or so for a few seconds then starts to fluctuate again.  I talked to Gerald and his opinion was that it was the alternator regulator.  Tried to google the alternator using the number on it and ebay has a separate regulator for it.  I've heard some have replaceable regulators and some don't.  I'm just learning this mechanic stuff so even though some things are obvious and you all are probably chuckling at my  hesitation to take the easy way...can it be this easy?  I have about 160 miles to drive today and maybe 300 miles this week before I will be in a position to try a fix myself.  Any comments, issues I should be aware of?   Batteries do not appear to be boiling off at this point.
Thanks
Jerry

[Mike Groves]

I am all ears waiting for what you find out about this.  Mine did this 3 years ago, had the alternator rebuilt, but it still was running too high and burned itself out again.  A second rebuild and the shop put limiters on its output because on the bench test it's output was expected 14.2V maximum but in the coach it was running over 15V output.  With the limiters I've been running it ok for over 2 years now.  While running along my Silverleaf notes between 12.8 and 13.2 volts.

Mike

[Gerald Farris]

Mike & Jerry,
You coaches have different alternator designs.

Mike's coach has a battery isolator with a Duvac alternator that depends upon a sense wire from the battery bank for it to determine the charge voltage at the battery. With this design, over charging can be a result of a bad sense wire or it's connection, or a bad voltage regulator.

In our phone conversation, Jerry said that his coach has a "Bird" system. With a "Bird" system, there is no sense wire because there is no battery isolator. The alternator is tied directly to the chassis batteries, and it's regulator uses the voltage in the output wire to determine the charge voltage. The house batteries are charged by the engine alternator only when the "Big Boy" solenoid is engaged by the "Bird" module.

So, as you can see from the system descriptions above, the two systems have a totally different design to determine the necessary charging voltage, Therefore, diagnosing a overcharging problem with the two systems has no relation from one to the other.

Jerry,
Your voltage regulator is replaceable, but be sure to double check the output cable connections and alternator ground cable connections first.

Gerald         

[steve zannella]

Hi Gerald

I'm reading this thread with interest as I have a similar problem except my dash lights and headlights flicker with engine running although I didn't notice any voltage changes. When this happens I turn on my generator and the flickering stops. Any ideas?

Steve

[Gerald Farris]

Steve,
If you have the inverter set to charge the batteries when the generator is started, from your description it sounds like you have an issue with your engine alternator since the flickering stops when the generator is started, but I would need to run some output test to be sure.

The reasoning that I used to come to that conclusion was the fact that the only thing that changes when the generator is started is that the inverter starts charging the batteries and stabilizes the voltage that the alternator should have been maintaining. Of course there are several things that can cause system voltage fluctuations but an alternator output test should verify the source.

Gerald   

[steve zannella]

Gerald

Yes the inverter was set to CHG. Also after driving for about an hour I turned off the generator and the lights didn't flicker. I have noticed this behaviour before and since had the alternator checked. No conclusions as to the problem. I now carry a spare alternator just in case.
Is there any harm to electronics with this problem or should I just replace the alternator to see what happens?

Steve

[Gerald Farris]

Steve,
The voltage fluctuation should not harm anything if it is staying within an acceptable voltage range, but since you do not know what the voltage fluctuation is, I can not answer that question. The fluctuation could have stopped because the batteries were fully charged and the voltage fluctuation was not higher than a fully charged battery or it might have stopped because the alternator voltage regulator was hot.

As for replacing the alternator without determining what the problem is, that may or may not correct the problem. However, I personally do not believe in throwing parts at a problem without diagnosing it first, but the odds are that you will fix the issue with a new alternator.

Gerald